Method and device for monitoring the movements of an actuator

ABSTRACT

A method of monitoring the motion of an actuator of a vehicle brake including establishing an actuator reference coordinate which is associated with a predetermined actuator reference position, defining an actuator actual coordinate in accordance with the actuator reference coordinate and in accordance with the motion of the actuator, establishing a first permitted actuator motion range from a permitted release end coordinate of the actuator for release of the brake and a first permitted brake application end coordinate of the actuator for application of the brake in accordance with the actuator reference coordinate and outputting a signal when the actuator actual coordinate lies outside the first permitted actuator motion range.

TECHNICAL FIELD

The present invention generally relates to monitoring devices and moreparticularly relates to a method and a device for monitoring the motionof an actuator of a vehicle brake.

BACKGROUND OF THE INVENTION

DE 197 14 046 A1 discloses an electromechanically operated wheel brakewherein an electric motor drives a rotating spindle. By way of atranslatory movement of the spindle induced thereby, the brake isactuated by displacement of the brake linings against the brake disc orbrake drum. In this arrangement, the spindle can move only within afixed mechanical range.

This range results from the constructive design of brake mechanics whichis normally rated so that the brake linings can be set or readjustedwithin a range of readjustment corresponding to lining wear in theirinitial position (release position). The setting is effected so that thebrake linings are at a given distance from, i.e., have a clearance to,the brake disc or brake drum. In the other direction, the mechanicalrange is rated so that lining replacement is easily possible when needed(i.e. the spindle can be withdrawn to a sufficient extent in thedirection of release of the brake).

To prevent the spindle from moving into abutment on the mechanical stopduring operation and, on the other hand, to recognize the necessity oflining replacement in due time, the relative drive or spindle movementcan be monitored.

An object of the present invention is to provide a method and a devicefor monitoring the motion of an actuator of a vehicle brake by whichmonitoring with respect to an absolute vehicle position is possible.

To monitor the spindle movement, magnets can be fitted to the drivingengine shaft in an evenly spread fashion which produce pulses whenpassing a Hall sensor fitted at an appropriate location. These pulsesare used to determine e.g. the course angle of the engine shaft relativeto a previously defined reference position. From this value, in turn,the translatory movement of the spindle can be inferred by way of thetransmission ratio between spindle rotation and spindle translation. Thereference position for this position measuring system which performsrelative and incremental measurement is fixed by zero pointinitialization, and changes of the course angle compared to thisreference position are reviewed by counting the pulses produced by theposition measuring system. Usually, the position of the drive shaft orof the spindle serves as a reference position, during which the brakelinings are in straight (i.e., force-free) abutment on the brake disc orbrake drum. The direction of motion of the drive can be sensed inaddition by an appropriately installed second Hall sensor. In this case,it applies in general to the counting direction that a mathematicallypositive angular variation implies a movement of the driving shaft inthe direction of brake application, and a negative angular variationmeans a movement in the direction of release of the brake.

However, the above system is a position measuring system with relativemeasurement, which determines spindle positions only relatively, withoutknowing which absolute position within the limited mechanical motionrange the spindle presently adopts.

Therefore, the following steps, the sequence of which is not determinedherein, will be performed according to the present invention:establishing an actuator reference coordinate associated with apredetermined actuator reference position, determining an actuatoractual coordinate in accordance with the actuator reference coordinateand in accordance with the motion of the actuator, establishing a firstpermitted actuator motion range based on a permitted release endcoordinate of the actuator for release of the brake and a firstpermitted brake application end coordinate of the actuator forapplication of the brake in accordance with the actuator referencecoordinate and issuing of a signal, when the actuator actual coordinateis outside the first permitted actuator motion range.

The term ‘actuator’ may refer to a moving part for actuation of thebrake. The moving part may e.g. be a motor shaft or a spindle. Theactuator is driven preferably electrically. The actuator position can besensed rotatorily and translatorily, however, it is preferred that it issensed rotatorily e.g. by means of a Hall sensor or a resolver. Thegiven actuator reference position is a fixed position which the actuatormay assume in a defined manner. That means, this position is an absoluteposition within the vehicle, preferably, within the vehicle brake andcan, thus, be always reassumed.

A switching sensor element such as a microswitch or a switching Hallsensor, which can sense the translatory position of the spindle, can beused to find the actuator reference position. When the actuator reachesthe actuator reference position predetermined by the sensor element, itwill issue a switching pulse or switch from the logical condition “0”into the logical condition “1”, for example. To adopt this position, theactuator preferably moves at a low speed in the direction of release ofthe brake until the sensor element signals that the position is reached,e.g. by the switching pulse.

Another possibility of finding the actuator reference position, withoutthe need of fitting an additional sensor element in the brake, mayinclude predefining the mechanical stop of the actuator on the enginehousing, preferably in the direction of release of the brake, asactuator reference position. To adopt this position, the actuator maypreferably move at a very low speed in the direction of release of thebrake. The engine current that drives the actuator, for example, will besensed during this movement. When the actuator moves against the enginehousing, the engine current will rise significantly because the engineoperates in opposition to a system with a very high amount of rigidityin this case. This current rise permits detecting that the actuatorreference position is reached and terminating the movement of theactuator.

A related actuator reference coordinate can be established at a givenactuator reference position. This can be done in that allocated to acounter, which is also used to determine the actuator actual coordinate,is a value which can be stored in a memory, or input from externally andstored subsequently. This value may equal zero so that the counter ise.g. simply reset or initialized again. Another possibility ofestablishing the actuator reference coordinate includes storing thevalue which is in the counter when the actuator reference position isreached as actuator reference coordinate. Attention should be paid, ifnecessary, when the actuator reference coordinate is established that,depending on the status of the actuator reference position, the counterstarting from the reference coordinate is in a position to count up anddown and produces utilizable values.

Further, a first permitted actuator motion range can be establishedwithin which the actuator is allowed to move. This permitted motionrange can refer to the position of the actuator or to the relatedcoordinate because one can be determined by the respectively other one.This first actuator motion range is confined by two permittedcoordinates, that is, by a permitted release end coordinate in thedirection of release of the brake, and by a first permitted brakeapplication end coordinate in the direction of application of the brake,the respective end coordinates pertaining to corresponding actuator endpositions. The first permitted actuator motion range is established inaccordance with the actuator reference coordinate and, thus, also inaccordance with the actuator reference position. Thus, a motion range isestablished which has an absolute reference to the actuator referenceposition.

The above-described method steps can be performed in a service brake ineach case when a vehicle is started. The corresponding coordinates canbe stored and polled again at any time. In a parking brake, these stepscan be performed when the brake is released which must be possible alsoduring travel of the vehicle. This can be done e.g. after first releaseof the brake after start of travel. For safety reasons, these steps canalso be performed several times during continued operation of thevehicle to check whether the coordinates found now as before arecoincident with the related positions. Thus, the actuator referenceposition can be assumed, and the actuator actual position can becompared with the actuator reference coordinate. A correction may becomenecessary due to wrong sensor pulses or a faulty transmission of thepulses (e.g. too many or too few pulses).

The proper monitoring of the motion of the actuator can be effected inthat an actuator actual coordinate is continuously determined as afunction of the motion of the actuator. The actuator actual coordinateand/or the actuator motion direction can be determined or detected byusing an incremental position measuring system of relative measurement.This determination can take place in that the counter, starting from theactuator reference coordinate, counts up or down the pulses of a Hallsensor installed at an appropriate location, depending on the directionof motion of the actuator. The direction of motion can be detected byusing an appropriately installed second Hall sensor.

The current actuator actual coordinate can be compared with thepermitted release end coordinate and the first permitted brakeapplication end coordinate, possibly, by taking into account thedirection of motion of the actuator to find out whether the actuatoractual coordinate lies outside the first permitted actuator motionrange. If this is the case, a corresponding signal will be issued.

The signal can be used to send an alarm to the driver. When the actuatoractual coordinate exceeds the first permitted actuator motion range inthe direction of release, this can be regarded as a malfunction of theengine because there might be the risk in this case that the spindlemoves against the engine housing. To prevent this action, the actuatorrelease motion can be stopped in addition to the output of the alarm.After the release movement of the actuator is terminated, severalsubsequent actions are possible such as a new initialization ordeactivation of the brake, etc.

When the actuator actual coordinate exceeds the first permitted actuatormotion range in the direction of brake application, an alarm can also besent to the driver indicating, for example, that brake liningreplacement is necessary.

Preferably, the permitted release end coordinate and the first permittedbrake application end coordinate are established with respect to themaximum possible mechanical actuator motion range, that means, they canbe so established that the spindle will not move against the mechanicalstop in the direction of release and will not move so far in thedirection of brake application that in the extreme case the metal of thebrake shoe will bear against the metal of the brake disc or brake drum,if brake linings no longer exist. Besides, corresponding safetydistances can be taken into consideration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an embodiment of the device of the presentinvention.

FIG. 2 shows exemplary variations of the brake actuation force withdifferent brake lining wear.

FIG. 3 is a flow chart of an embodiment of the method of the presentinvention.

FIG. 4 is a flow chart of another embodiment of the method of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an exemplary embodiment of a control device 100 of thepresent invention which can be a microprocessor, for example, configuredto perform the steps in FIGS. 3 and 4. Device 100 has an input 106 e.g.for data input. By this, the actuator reference coordinate can be inputwhich can be assigned by the actuator to a counter comprised in thecontrol device 100 when the actuator reference position is reached.Further, the maximum possible mechanical end positions of the maximumpossible mechanical motion range can be input with respect to theactuator reference position, from which, in turn, the end coordinatescan be determined. Also, signals of other devices can be input by way ofinput 106 for processing in the control device 100.

The control device 100 controls the actuator motion, for example, byoutputting control signals through output 105. Device 100 is connectedto a current sensor 101 which senses the engine current that is used todrive the actuator. When the actuator has reached the actuator referenceposition, i.e., the mechanical stop of the spindle on the enginehousing, for example, the current sensor 101 will signal a significantcurrent rise to the control device 100. The latter knows in this eventthat the actuator has reached the reference position and may then assignthe corresponding actuator reference coordinate, which e.g. was input byway of input 106, to the counter.

During motion of the actuator, a position sensor 102 passes pulses tothe control device 100 which the counter uses for counting. Either theposition sensor 102 can furnish an information about the direction ofmotion of the actuator, or the control device 100 can receive thisinformation in another way.

Further, the control device 100 determines the first permitted actuatormotion range with respect to the actuator reference coordinate, e.g., byusing input end positions. The permitted release end coordinate and thefirst permitted brake application end coordinate can be stored in amemory within the control device 100 so that they can be polled anytime. Provided the actuator reference coordinate is input by way ofinput 106, it is, however, also possible to also input the previouslyestablished end coordinates through this input 106. This could happenone time during initialization and need not be repeated then. Thispossibility is e.g. advisable when the actuator motion range isestablished as a function of the mechanically possible motion range ofthe actuator because in this case the actuator reference position andthe mechanical motion range are known already in advance. In this event,the actuator reference coordinate and the end coordinates can bedetermined one time already in advance.

A comparison device can be provided in the control device 100 to comparethe actuator actual coordinate with the release end coordinate and thefirst brake application end coordinate and, possibly, furthercoordinates, whereupon the control device 100 can find out whether theactuator actual coordinate lies outside the first permitted actuatormotion range. If this is the case, the control device will output acorresponding signal. This signal can be sent to the warning indicator103, which can warn audibly and/or visually, and/or also tactilely, onthe one hand, and to the lining wear indicator 104 as a function of thecomparison between the actuator actual coordinate and the firstpermitted actuator motion range, on the other hand. The warningindicator can be subdivided into single ranges which react to differentsignals of the control device to be able to indicate to the driver, forexample, whether the first brake application end position or the releaseend position or the respective coordinate was reached. The attaining offurther brake application end positions outside the first permittedactuator motion range which can be input or determined in a similarfashion as the first brake application end position or coordinate (andwhich will be described hereinbelow) can also be indicated by way of thewarning indicator.

The initial position (clearance position) of the brake linings or of theactuator can be established again during operation of the brake independence on the duration of operation. To this end, a position can beassumed with the actuator where the brake linings abut on the brake discand/or the brake drum in a force-free manner. A corresponding actuatorreference coordinate may then be assigned to this actuator referenceposition. In dependence on the brake lining wear, another actuatorreference position may then be assumed operation-responsively, and anactuator reference coordinate can be adapted or assigned anewaccordingly. The result is that brake lining wear can be determined fromthe reference coordinate. The control device 100 will then deliver acorresponding signal to the lining wear indicator 104 which informs thedriver e.g. audibly and/or visually about brake lining wear. Theclearance is then adjusted in dependence on the reference position orreference coordinate.

Three exemplary diagrams with variations of the brake actuation force Fas a function of the position x of the actuator are shown schematicallyin FIG. 2. A different reference position is respectively shown in eachdiagram. The reference position with new non-abraded brake linings XREF0is referred to in FIG. 2A. The minimum position XMIN on the left-handside in the diagram illustrates the mechanical stop of the actuator inthe direction of release. The maximum position XMAX on the right-handside in the diagram represents the position where e.g. the metal of thebrake shoe would come to bear against the metal of the brake disc orbrake drum in case the brake linings would have been worn completely.The minimum and maximum positions XMIN and XMAX represent the limits ofthe maximum possible mechanical actuator motion range. The position XLEdesignates the release end position which must not be exceeded by theactuator e.g. in the direction of release of the brake. The positionXZE1 refers to the first brake application end position. The release endposition and the brake application end position XLE and XZE1 enclose thefirst permitted actuator motion range within which the actuator isallowed to move. The position XLS0 represents the clearance position ofthe brake with brake linings not worn. When the brake is actuated untila maximum force, the result is the illustrated force variation. Thelatter ends in FIG. 2A with the maximum force in the maximum forceposition XFMAX0. The range between the reference position XREF0 and themaximum force position XFMAX0 represents the operating range of thebrake, i.e., the range where compression of the brake linings ispossible.

A reference position XREF1 is shown in FIG. 2B where the brake liningsare worn to such an extent that replacement should be effected. Thisfact is indicated by the actuator exceeding the first brake applicationend position XZE1 with maximum brake actuation force. An alarm is sentto the driver when the first brake application end position XZE1 isreached in this embodiment. However, normal braking is still possible ascan be seen in the force variation.

In FIG. 2C, the brake linings are worn to such an extent that theactuator reaches a second brake application end position XZE2 which mustnot be exceeded. However, to permit at least slight braking with thisbrake continuously, the actuator is maintained in this brake applicationend position XZE2, with the result that the maximum possible brakeactuation force F is no longer reached. When the method is applied toboth wheels of an axle, it is possible that the brake force isdistributed differently onto the two wheels when the brake linings aredifferently worn. In this event, the control device 100 can be soconfigured as to control the brake force distribution of the two wheelsso that the vehicle will not deviate from its track. It is possible thatthe brake is assisted by another hydraulic brake, for example. An alarmwhich is triggered when the first brake application end position XZE1 isreached may then be modified correspondingly to indicate when the secondbrake application end position XZE2 is reached. With the decrease of thebrake actuation force, the actuator can also be moved correspondingly inthe direction of release again, and the alarm can be indicatedcontinuously and, possibly, can be indicated again also during restartof the vehicle.

The third brake application end position XZE3 shown in the diagrams,which is disposed on the right side of the second brake application endposition XZE2 or can be equal to this position in another embodiment,represents that actuator position where the brake is deactivated e.g.simultaneously with the output of an alarm because the actuator hasreached this position e.g. due to a malfunction. The second and thirdbrake application end positions XZE2, XZE3, exactly as the release endposition XLE and the first brake application end position XZE1, areestablished preferably in accordance with the maximum possiblemechanical actuator motion range.

The diagrams of FIG. 2 are schematic views showing only one embodimentof several. The reference position with non-abraded linings XREF0 can beassumed, for example, as an exchange position for replacement of a brakelining. Any other appropriate position is, however, also possible. Thecorresponding actuator exchange coordinate can then be determined andstored e.g. in the control device 100. The illustrated diagrams can alsobe regarded as a representation of the force variations in dependence onthe corresponding coordinates. Then, the illustrated quantities x, etc.,should be considered as coordinates or counter values.

FIG. 3 shows as an example the sequence in an embodiment of the methodof the present invention where initially the actuator position isassumed in step 300. A polling is made in step 301 whether the actuatorreference position has already been reached. If this is not the case,the actuator reference position is continuously assumed in step 300.When the actuator reference position is reached, the related actuatorreference coordinate is determined in step 302. Subsequently, thepermitted actuator motion ranges inclusive the release end position andthe first to third brake application end positions are established instep 303. Now the actuator actual coordinate corresponding to thecurrent position of the actuator can be determined for the actualoperation of the brake.

Following is step 305 in FIG. 3B where a polling is performed as towhether the release end coordinate in the direction of release wasreached by the actuator actual coordinate. If this is the case, acorresponding alarm is output in step 306 and a release motion of theactuator is terminated in step 307. If the release end coordinate is notreached, a polling is performed in step 308 whether the first brakeapplication end coordinate in the direction of brake application wasreached by the actuator actual coordinate. If this is not the case, theprocess is continued in step 304. When the polling is affirmed, acorresponding alarm is output in step 309 and, thereafter, a polling isperformed in step 310 whether the second brake application endcoordinate in the direction of brake application was also reached by theactuator actual coordinate. If this is not the case, the process iscontinued in step 304.

When the polling in step 310 of FIG. 3B is affirmed, the process iscontinued in step 311 of FIG. 3C. There, the actuator is maintained inthe second brake application end position and a polling is performed instep 312 whether the actuator actual coordinate contrary to step 311 hasreached the third brake application end coordinate in the direction ofbrake application. In the negative, the process is continued in step304. When the result of polling is positive, a corresponding alarm isoutput in step 313, and in step 314 the brake is deactivated and theprocess terminated. Subsequently, a primary control such as an ESPcontrol could take care of the further brake operation, for example.

Steps to determine and indicate lining wear are listed in FIG. 4. Theactuator reference position is assumed in step 400. The associatedreference coordinate is thereafter stored in step 401. This includes aprevious determination of the reference coordinate with the actuatoractual coordinate. Subsequently, lining wear as a function of thereference coordinate is established in step 402. Lining wear or arelated quantity is indicated or advised audibly and/or visually to thedriver in step 403.

The steps illustrated in FIG. 4 can be performed in different points ofFIG. 3. However, this action should not be conducted when the brake isreleased in order to prevent interruption of the brake operation.Besides, the steps of FIG. 4 can be repeated in case of need, andadjustment of the clearance can follow directly so that the brake canadopt a correct initial position. Implementation could be such that incase one or more conditions are satisfied, the method steps 400 to 403are performed before step 304 in FIG. 3A.

For brake lining replacement, an operating element (such as a switch) tobe actuated by the driver can be provided in the vehicle interior.Subsequently, the actuator will automatically adopt the replacementposition. When lining replacement is completed, the switch can beactuated again or released again, which may then have as a result e.g. anew initialization of the reference position or determination of thereference coordinate. The actuator can then adopt the clearanceposition, whereby the brake would be ready for operation again.

What is claimed is:
 1. Method of monitoring the motion of an actuator ofa vehicle brake, including the steps of: establishing an actuatorreference coordinate related to a predetermined actuator referenceposition, determining an actuator actual coordinate in accordance withthe actuator reference coordinate and in accordance with the motion ofthe actuator, establishing a first permitted actuator motion range froma permitted release end coordinate of the actuator for releasing thebrake and a first permitted brake application end coordinate of theactuator for application of the brake in accordance with the actuatorreference coordinate, and outputting a signal when the actuator actualcoordinate lies outside the first permitted actuator motion range,establishing a second permitted actuator motion range from the permittedrelease end position and a second permitted brake application endposition, wherein the first actuator motion range lies within the secondactuator motion range or is equal to it.
 2. Method as claimed in claim1, wherein the step for determining the actuator actual coordinatefurther includes identification of the direction of motion of theactuator.
 3. Method as claimed in claim 1, further including outputtingan alarm whenever the actuator actual coordinate in the direction ofbrake application exceeds the first brake application end coordinate. 4.Method as claimed in claim 1, wherein an alarm is output to the driverwhenever the actuator actual coordinate in the direction of releaseexceeds the release end coordinate.
 5. Method as claimed in claim 1,wherein the actuator is driven electrically.
 6. Method as claimed inclaim 1, wherein the step of establishing the actuator referencecoordinate further includes moving the actuator to adopt the actuatorreference position and identifying that the actuator reference positionis reached by the actuator.
 7. Method as claimed in claim 6, wherein theactuator reference position is predetermined by the position of aswitching sensor which outputs a corresponding switch signal fordetecting that the actuator reference position is reached when theactuator has reached this position.
 8. Method as claimed in claim 1,wherein an absolute reference position is predetermined by one of thelimits of the maximum possible mechanical actuator motion range. 9.Method as claimed in claim 8, wherein the step of establishing theactuator reference coordinate further includes detecting an enginecurrent that drives the actuator in order to detect that the actuatorhas reached the actuator reference position.
 10. Method as claimed inclaim 1, wherein the actuator actual coordinate or the direction ofmovement of the actuator are determined or detected by using anincremental position measuring system with relative measurement. 11.Method as claimed in claim 1, wherein the step of determining anactuator reference coordinate includes determining, repeatedly saidactuator reference coordinate for an actuator position in which thebrake linings bear against the brake disc or the brake drum in aforce-free manner.
 12. Method as claimed in claim 11, wherein the brakelining wear is determined in accordance with the actuator referencecoordinate.
 13. Method as claimed in claim 12, wherein a quantitycorresponding to the brake lining wear is transmitted to the driverauditively or visually.
 14. Method as claimed in claim 11, wherein thelining clearance is adjusted in accordance with the actuator referencecoordinate.
 15. Method as claimed in claim 11, further including thestep of establishing an actuator exchange coordinate in accordance withthe corresponding actuator reference coordinate which is determined whenthe brake linings are not worn, and the associated actuator exchangeposition is assumed when a brake lining shall be replaced.
 16. Method asclaimed in claim 1, wherein the first or the second permitted actuatormotion range is established in accordance with the maximum possiblemechanical actuator motion range.
 17. Method as claimed in claim 1,wherein when the actuator actual coordinate in the direction of brakeapplication reaches the second brake application end coordinate, theactuator is retained in the associated brake application end positionuntil the brake is released.
 18. Method as claimed in claim 1, furtherincluding the step of deactivating the brake or activating an alarm whenthe actuator actual coordinate in the direction of brake applicationreaches a third brake application end coordinate which, in the directionof brake application, lies outside the second actuator motion range oris equal to the second brake application end coordinate.
 19. Method asclaimed in claim 17, further including applying simultaneously to twowheel brakes of the same axle, the brake force distribution of the twowheels such that the vehicle does not deviate from its track.